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NEON DATA
Hi All,
I made a few measurements on a Jefferson 15,000 volt, 60 mA
neon sign transformer:
Secondary resistance of terminal 1(near ground lug) : 3.375 Megohm
Secondary resistance of terminal 2(near 120V terminals): 4.2 Megohm
Inductance: meter went beserk. Couldn't get a reading!
For the next measurement I connected two different capacitors between
the signal generator and terminal 2 (used for all measurements). The other
lead of the signal generator was grounded to the transformer case. An
oscilloscope was connected between terminal 2 and the transformer case.
C Fr
0.1uF 30Hz
0.01uF 105Hz
Then I used Howe's method (page 453 of Radiotron Designers Handbook
4'th edition) plotting C VS 1/Fsquared to find the self capacitance using
the x intercept formula x = (x1y2 - x2y1)/(y2 - y1) where
y2 = 1/(30 squared) = .00111
x2 = .1uF
y1 = 1/(105 squared) = .000090702
x1 = .01uF
x = ((.01uF X 0.00111) - (.1uF X 0.000090702)) / (0.00111 - 0.000090702)
= 2.002 nanoFarads
Then I performed the following calculations using the simplified formula
for inductance (the high resistance tends to make this slightly inaccurate):
L = 1/(2 X PI X frequency X capacitance) where capacitance = Cself of coil
+ C(required to resonate)
Fr L
105Hz 191.4 Henrys
30Hz 275.92 Henrys
Can this be done this way? If not please correct me!
The next set of measurements were performed to ascertain the effect of
various
inductors, capacitors, and resistors hung off the high voltage terminal of
the
transformer. Terminal 2 was used. The setup consisted of the following:
A 200,000 Volt diode was connected from the high voltage lead of the
transformer to a 3 Megohm resistor which was connected to one terminal
of a 0.1 uF, 25 kV capacitor. The other terminal of the capacitor was
connected
to ground. A dump switch was connected between the hot end of the capacitor
and ground for safety. The hot end of this capacitor was also connected to
a high voltage voltmeter with an input impedance of 1 Gigohm (Collmer
Semiconductor, Inc, "Digital H.V. meter" Model # CS5190A1) to act as a
peak reading DC voltmeter. All high voltage DC measurements (HVDC)
were made this way. AC measurements (HVAC) were made with a Hipotronics
high voltage probe (Model #: KVM-200D, part #: 45-125 (used the stack only))
with a maximum frequency of 1Khz, an impedance of 750 Megohm, and a
ratio of 2000 to 1. The Hipotronics probe was connected to an oscilloscope.
The ground side of the probe was connected to the grounded case of the
transformer. Measurements from the scope (1 Megohm, AC coupling)
were made with automatic cursor lines with direct digital readout.
For the first measurement I connected the Hipotronics probe directly to the
high voltage terminal 2 of the transformer to measure the transformer
voltage
without anything else attached to it:
input VAC HVDC output HVAC output scope waveform description
118 10.7 kV 9.75 V P-P 60 Hz
sine wave
For the next set of measurements I connected various doorknob capacitors
and a 300mH torroidal inductor (1" id X 2" od X 1/2 " thick + 40 turns of
#16
magnet wire) directly from the high voltage terminal 2 to ground. Where the
inductor was used it was connected between the terminal 2 and the capacitor.
Lower voltages were used to protect the transformer (except in one
instance).
All HVAC measurements must be multiplied by 2000 to get true reading :
input VAC HVDC output HVAC output scope waveform description
capacitor value inductor
112.7 10.7 kV 10.18 V P-P distorted 60 Hz
sine wave 500 pF none
almost triangular with a
shoulder near the peak
112.9 10.7 kV "
same as above 500 pF
300 mH
112.2 10.7 kV " same
as above with probe 500 pF 300 mH
connected to where the
inductor and capacitor
connect together
-no difference from inductor-
112.7 12.7 kV none brought
voltage up and 1 nF none
(ouch!)
then down too quickly to
get a scope reading.
didn't want to cook transformer.
(wicked buzzing sound inside the transformer)
100.7 10.7 kV " pure
60 Hz triangle wave 1 nF none
(buzzing sound from
transformer)
100.5 10.7 kV "
same as above 1 nF
300 mH
-no difference from inductor-
100.7 10.7 kV " same
as above 1 nF 300 mH
(at 118 VAC input
connected to where the
this would be
inductor and capacitor
14.5 kV peak!)
connect together
-no difference from inductor-
86.9 10.7 kV 9.68 V P-P distorted
squarish sine 2 nF none
wave with shoulders at
3.1875 V P-P on one side
105.2 10.7 kV 9.44 V P-P same as
above with a 3 nF none
more square wave like
appearance with shoulders
at 7.125 V P-P on one side
109.3 10.7 kV 9.31 V P-P same as above
with a 4 nF none
very square wave like
appearance with shoulders
at 8 V P-P on one side
109.3 10.7 kV " same
as above 4 nF 300 mH
-no difference from inductor-
For the next measurements I tried clamping the voltage with varisters:
118.4 9.3 kV "
same as above with a 1 nF
none
very square wave like
stack of 10 (800 V) varisters in series appearance with
notched
HV output terminal 2. got very hot spike like
shoulders
101.9 10.7 kV " pure
60 Hz triangle wave 1 nF none
stack of 12 (800V) varisters in series -no clamping
action-
across HV output terminal2. got
slightly warm to touch
For the next set of measurements I tried various resistors in series with
the HV terminal 2.
The resistances were made up of combinations of 2 watt carbon composition
resistors to
keep down the voltage stress:
87.6 10.7 kV 9.75 V P-P triangle
wave with shoulders 2 nF none
at 3.437 V P-P
1 k ohm resistor
87.6 10.7 kV "
same as above but with 2 nF
none
HVAC probe connected
1 k ohm resistor at
junction of resistor and
capacitor
87.6 10.7 kV 9.75 V P-P triangle
wave with shoulders 2 nF none
at 3.437 V P-P
5 k ohm resistor
98 10.7 kV 9.56V P-P triangular
sine wave 2 nF none
100 k ohm resistor
These measurements would indicate that the only way to protect the neon sign
transformers high voltage output
from itself would be to put a series of humongous varisters and or safety
gap across it. A 5 kohm resistor with
RF inductor + 500pF bypass capacitor + another RF inductor (to keep the
bypass capacitor out of the tank circuit)
might be a good combination to keep the RF out of the transformer. Will try
to measure this combination when I
complete my small measurable (portable) Tesla coil.
All of these measurements were made with only ONE UNLOADED HV terminal to
see what the voltage
might become if the spark gap on the Tesla coil primary were opened too
wide.
Hope that these few measurements may be useful to everyone.
Barry